<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn" >点我创建一个input框</button>
    <script>
         document.querySelector('#btn').onclick=()=>{
            const input=document.createElement('input');
            input.style.backgroundColor='red'
            input.parentElement.style.backgroundColor='black';
            input.focus();
             document.body.appendChild(input);
            //  input.focus();
            // input.parentElement.style.backgroundColor='black';

         }
    </script>
</body>
</html>